1. Field of the Invention
The invention relates to the area of turbomachines, in particular turbojet engines in aircraft.
2. Description of the Related Art
A turbojet engine conventionally comprises a plurality of component parts such as a compressor, a combustion chamber and a turbine. During its operation, the turbojet engine is subjected to wear which affects its performance and may lead to the appearance of failures in one or more component parts of the turbojet engine in the event of abnormal or unforeseen wear. The turbojet engine and the aircraft are not functional in the event of a failure, which poses a problem. Failures are generally associated with phenomena of fouling, corrosion, oxidation, erosion, abrasion or even the ingestion of a foreign body, problems with measurements and problems with computers, etc.
In order to prevent the appearance of a failure, inspection operations on the turbojet engine are programmed at regular intervals. It is thus possible to detect whether one of the component parts of the turbojet engine is defective or exhibits symptoms heralding a future failure Such a method for the detection of failures is not satisfactory, since the wear in turbojet engines of the same family is variable, given that an inspection at regular intervals is not adequate. In fact, if the frequency of the inspections is too low, the risk of failure is increased. If the frequency of inspection is too high, on the other hand, an inspection step may be implemented at a time when the engine is in perfectly good condition, which is a waste of time.
Continuous monitoring, that is to say for each flight cycle of the aircraft, of the individual performance parameters of a turbojet engine in order to detect the appearance of failures in the turbojet engine at an early stage has been proposed in order to eliminate this problem.
Already familiar from the prior art is a method for the detection of failures for a turbojet engine, in which use is made of a database of known failures that have been identified throughout the life of turbojet engines belonging to the same family. By way of example, the fuel delivery rate, the speed of the turbojet engine and the temperature at the outlet from the engine have been measured by a computer mounted on the turbojet engine. In the event of the appearance of a failure in the engine, the parameters measured by the computer are stored in a database in association with an identifier of failure. By way of example, if the turbine of the turbojet engine is defective, the values for the parameters of the fuel delivery rate, the speed of the turbojet engine and the temperature at the outlet from the engine that have been measured by the computer prior to the appearance of the failure are stored in the database of failures, and in this case a failure of the turbine of the turbojet engine is associated with the aforementioned values of the parameters for the identifier of failure.
The database is created on the basis of a large number of measurements obtained by feedback in the course of flights by turbojet engines of the same family and by the analysis of the failures of the said turbojet engines. In practice, several thousands of flight hours are necessary in order to obtain a relevant database. To detect a failure of the turbojet engine at an early stage, it is sufficient to compare the values of the actual parameters for a turbojet engine with the values of the parameters in the database of failures in order to deduce the next failure of the turbojet engine by reading the identifier of failure in the database of failures.
It will be readily appreciated that the relevance of this method of detection depends on the size and the quality of the database. The greater the level of feedback, the greater the relevance of the detection of failure will be.
Such a method is thus appropriate for the standard turbojet engines that have been in service for a number of years, but is inappropriate for new turbojet engines having only a few flight hours. The expression “new turbojet engine” is used here to denote both a development of a standard turbojet engine and a turbojet engine of an entirely different type.
A further disadvantage of a method for the detection of failure according to the prior art is that it does not permit a precise indication to be given of which particular component part of the turbojet engine is defective as a consequence of the use of a reduced number of sensors on the turbojet engine while the aircraft is in flight. As a result, when a failure is detected, maintenance may be carried out on a large number of component parts of the turbojet engine although only a single component part is defective.